Other switches are available for such purposes, e.g. mercury switches and pressure switches, but these are not as reliable and are more expensive than reed switches. Furthermore, such known switches have been found to be inaccurate and variable in operation to an unacceptably wide degree.
Reed switches are cheap, highly reliable and accurate, but suffer from the disadvantages that they have a small differential between the switch being activated to the "on" position and de-activated to the "off" position, or vice versa. Thus, if they are float operated they can be used to detect only a very small change in liquid level.
An object of the present invention is therefore to obviate or mitigate the aforementioned disadvantages by providing means whereby a float-operated reed switch or float switch can detect greater differences in liquid levels than is possible with existing float-operated reed switches.